17α-estradiol, a lifespan-extending compound, attenuates liver fibrosis by modulating collagen turnover rates in male mice
BackgroundEstrogen signaling is protective against chronic liver diseases, although men and a subset of women are contraindicated for chronic treatment with 17{beta}-estradiol (17{beta}-E2) or combination hormone replacement therapies. We sought to determine if 17-estradiol (17-E2), a naturally-occurring diastereomer of 17{beta}-E2, could attenuate liver fibrosis. MethodsWe evaluated the effects of 17-E2 treatment on collagen synthesis and degradation rates using tracer-based labeling approaches in male mice subjected to carbon tetrachloride (CCl4)-induced liver fibrosis. We also assessed the effects of 17-E2 on markers of hepatic stellate cell (HSC) activation, collagen crosslinking, collagen degradation, and liver macrophage content and polarity. FindingsWe found that 17-E2 significantly reduced collagen synthesis rates and increased collagen degradation rates, which was mirrored by declines in transforming growth factor {beta}1 (TGF-{beta}1) and lysyl oxidase-like 2 (LOXL2) protein content in liver. These improvements were associated with increased matrix metalloproteinase 2 (MMP2) activity and suppressed stearoyl-coenzyme A desaturase 1 (SCD1) protein levels, the latter of which has been linked to the resolution of liver fibrosis. We also found that 17-E2 increased liver fetuin-A protein, a strong inhibitor of TGF-{beta}1 signaling, and reduced pro-inflammatory macrophage activation and cytokines expression in the liver. InterpretationWe conclude that 17-E2 reduces fibrotic burden by suppressing HSC activation and enhancing collagen degradation mechanisms. Future studies will be needed to determine if 17-E2 acts directly in hepatocytes, HSCs, and/or immune cells to elicit these benefits. FundingThis work was supported by the US National Institutes of Health and US Department of Veterans Affairs. RESEARCH IN CONTEXTO_ST_ABSEvidence before this studyC_ST_ABSThe prevalence and severity of chronic liver diseases are greater in men than women and men are twice as likely to die from chronic liver diseases. However, the prevalence and severity of nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), and liver fibrosis becomes comparable between the sexes following menopause, particularly when hormone replacement therapies (HRT) are not initiated. These observations suggest that estrogen signaling is protective against liver disease onset and progression, which is supported by studies in rodents demonstrating that 17{beta}-estradiol (17{beta}-E2) ameliorates hepatic steatosis and fibrogenesis. However, chronic administration of 17{beta}-E2 or combination HRTs are unrealistic in men due to feminization and increased risk for stroke and prostate cancer, and a subset of the female population are also at an increased risk for breast cancer and cardiovascular events when on HRTs. Therefore, we have begun exploring the therapeutic potential of 17-estradiol (17-E2), a naturally-occurring, nonfeminizing, diastereomer of 17{beta}-E2, for the treatment of liver diseases. Added value of this studyIn this study, using tracer-based labeling approaches in male mice subjected to CCl4-induced liver fibrosis, we show that 17-E2 reduces liver fibrosis by attenuating collagen synthesis and enhancing collagen degradation mechanisms. Both transforming growth factor {beta}1 (TGF-{beta}1) and lysyl oxidase-like 2 (LOXL2) protein content in liver were reduced by 17-E2. We also found that 17-E2 increased matrix metalloproteinase 2 (MMP2) activity and suppressed stearoyl-coenzyme A desaturase 1 (SCD1) protein levels, the latter of which has been linked to the resolution of liver fibrosis. We also found that 17-E2 increased liver fetuin-A protein, a strong inhibitor of TGF-{beta}1 signaling, and reduced pro-inflammatory macrophage activation and cytokine expression in the liver. Implications of all the available evidenceThis study supports the idea that estrogens are protective against chronic liver diseases and that 17-E2 may have therapeutic utility for the treatment of liver fibrosis.